Background: Many patients with obsessive-compulsive disorder (OCD) do not receive first-line treatment according to the current guidelines (cognitive behavioral therapy with exposure and response prevention, CBT with ERP) due to barriers to treatment. Internet-based therapy is designed to overcome these barriers. The present study evaluates the efficacy of an Internet-based writing therapy with therapeutic interaction based on the concept of CBT with ERP for patients with OCD. Methods: Thirty-four volunteers with OCD according to DSM-IV-criteria were included in the trial and randomized according to a waiting-list control design with follow-up measures at 8 weeks and 6 months. The intervention consisted of 14 sessions, either starting directly after randomization or with an 8-week delay. Main outcome measure was the change in the severity of OCD symptoms (Yale-Brown Obsessive Compulsive Scale Self- Rating, Y-BOCS SR, and Obsessive-Compulsive Inventory-Revised, OCI-R). Results: Obsessive-compulsive symptoms were significantly improved in the treatment group compared to the waiting-list control group with large effect sizes of Cohen's d = 0.82 (Y-BOCS SR) and d = 0.87 (OCI-R), using an intention-to-treat analysis. This effect remained stable at 6-month follow-up. Only 4 participants (12%) dropped out prematurely from the study. Of the 30 completers, 90% rated their condition as improved and would recommend the program to their friends. Conclusions: Internet-based writing therapy led to a significant improvement of obsessive-compulsive symptoms. Even though replications with larger sample sizes are needed, the results support the notion that Internet-based approaches have the potential for improving the treatment situation for patients with OCD.
